1. Field of the Invention
This invention relates to a battery device and more particularly to a battery device having battery-protective parts connected to secondary batteries, such as nickel cadmium batteries or lead batteries.
2. Description of the Prior Art
FIG. 1 is a perspective view of a prior art battery device which is of interest to this invention, said battery device being shown with an upper case member 1 separated from a lower case member 2. The upper and lower case members 1 and 2, when fitted together, form a case. The lower case member 2 receives two cylindrical battery assemblies 3 and 4 arranged side by side in contact with each other. The battery assemblies 3 and 4 each comprise a plurality of unit batteries 5, such as cylindrical nickel cadmium batteries. The unit batteries 5 are connected in series with each other and covered with a paper tube 6, forming the mechanically integrated battery assemblies 3 and 4. The battery assemblies 3 and 4 are connected in series with each other by a connector plate 7. The series-connected battery assemblies 3 and 4 have lead wires 8 and 9 connected to the cathode and anode thereof, respectively. The lead wires 8 and 9 are led out of the case through a notch 10 formed in the upper case member 1. The front ends of the lead wires 8 and 9 are formed with a connector, not shown.
One lead wire, e.g., 8, has a temperature fuse 11 and a current fuse 12 placed therein as battery-protective parts. The temperature fuse 11 protects the batteries from thermal influences due to a sharp increase in battery temperature during charging caused as by overcharge. Thus, it detects a predetermined temperature, whereupon it cuts off the circuit. The current fuse 12 protects the batteries from thermal influences due to an abnormal temperature rise caused by a large current flowing through the circuit as when a short circuit takes place in the external circuit. Thus, it detects a predetermined current, whereupon it cuts off the circuit. In this manner, protection of the batteries from thermal influences is provided in two ways, temperature detection and current detection.
In the device shown in FIG. 1, however, once an abnormality takes place, the circuit remains broken and it is necessary to replace the battery-protective part each time before the device can be used again. With this taken into account, it is seen that the arrangement must be such as to allow easy access to the temperature fuse 11 and current fuse 12. To this end, an arrangement is employed as an example wherein the upper case member 1 is formed with a window 13 to provide easy access to the fuses 11 and 12. This window 13 is normally closed by a label 14, which will be removed when necessary. Alternatively, if the upper case member 1 is secured to the lower case member 2 by screws (not shown) so that the upper case member 1 can be separated from the lower case member 2 as needed, easy access to the fuses 11 and 12 can be gained. Even if these arrangements are employed, however, it is very troublesome to replace the battery-protective parts and many manufacturers and sellers would not like to assume the duty of maintenance thereof.
Another prior art technique is U.S. Pat. No. 3,518,524 "Cordless Electric Appliance" granted to Roszyk. This patent discloses an arrangement comprising a thermostat switch mounted on the sheath of a secondary battery; thereby detecting heat generation in a charging period to cut off the charging current in the charging period, automatically continuing and discontinuing the charging operation. This thermostat switch, however, is absolutely for the purpose of charge control, never serving as a safety device when some failure occurs. More particularly, in order to provide such safety device, a device for detecting the battery temperature and current must be provided not only in the charging circuit but also in the discharging circuit.